When you power it on, it should be in whatever setting you left it in. To set in auto mode, turn it on and then hold the up arrow until the dot flashes three times. To disable auto mode, hold the down arrow until the dot flashes twice. If you take it out of auto mode, you will have ten intensity settings you manually adjust by the up or down arrows. Whatever seething of the ten you choose, it will return to when turned off or on. I like the auto because it will compensate for early morning light to midday sun etc...